ASI1600mm cool

[wimvb]

Unfortunately not a match to my bank account, $ 475 vs £ 125 . But just comparing the curves, they seem to have much better Oiii coverage and also much better sodium rejection. I would also expect the astrodon filters to be more uniform from set to set. The sodium rejection gap of zwo filters is very narrow and on the edge of the red and green curves. This makes it very sensitive to production fluctuations.

[Gina]

Maybe the ZWO RGB matched filter set would be better than the Baader set I have ATM for the ASI1600MM-Cool.  I might think about that for when the galaxy season comes round.

[Gina]

I see FLO are selling a NEW Baader LRGB filter set with a narrower green band than my earlier set, at least as far as I remember.  I feel sure the older Baader set have pretty much equal bands for the three colours.  I have not really tried my Baader RGB filters with the ASI1600MM-Cool - the weather didn't let me last galaxy season.  At £125 the ZWO filters look affordable and the spec looks good.  From the excellent impression I have had with ZWO kit I reckon their LRGB filter set could be a good buy.  I see they also do an IR pass filter which is interesting.

[wimvb]

1 hour ago, Gina said:

Maybe the ZWO RGB matched filter set would be better than the Baader set I have ATM for the ASI1600MM-Cool.  I might think about that for when the galaxy season comes round.

When I bought the zwo asi 174mm, I also got the standard lrgb filters. Since then I've done the math and calculated the best exposure ratios between r, g, and b. In retrospect, I should have also done that for the asi1600 optimised filters, to compare.

Anyway, I found the ratios to be 145:100:107, for r:g:b. I.e. red needs 45% longer single frame exposures than green to get a proper colour balance from a white light source. The problem is that if I use this and shoot different exposures, I will also need to do different darks. That's the whole reason for getting optimised filters in the first place.

The Astrodon filter sets e-series and i-series are designed for red and green sensitive chips, respectively. You'd have to do the math to match the filters to any camera.

On casual inspection, the (new?) Baader set seems to be similar to the ZWO optimised, with two exceptions:

1. The green and blue filters overlap at Oiii, while H-b signal ends up in the blue channel only. (Good thing)

2. The red and green have a larger overlap at the sodium line. (Bad thing)

Based on filter curves alone, the Baader set may actually be poorer than ZWO in handling light pollution, and the Astrodon should outperform both (it better, at that price).

But beware, this comparison is solely based on published filter curves, NOT on actual experience, mechanical stability, reflection properties, or other optical characteristics.

[Gina]

I have negligible light pollution here so that is not a problem.  From a practical point of view having equal exposures for all three colours would be nice but another thought comes to mind, how does the bandwidth of each colour affect the colour result?  Empirically one would think equal bandwidths might be best but I guess it depends on what we are comparing with.  Does the colour balance really matter assuming that exposures are adjusted to make white light appear white?  In view of what we do with NB imaging I would think not.  The general idea seems to be to make the prettiest picture   And to bring out the dark banding and other details.  I guess the only way to find out would be to compare results from both filter sets.  Oh, and I plan to add in Ha to the RGB (if that makes any difference to the RGB wavebands used).

[wimvb]

The "compare-the-curves" exercise is strictly only valid for a single frame (= 3 exposures) white light source, without any weight factors in creating the rgb image. DSO imaging is an entirely different beast.

The Astrodon I-series red filter looks much more orange than the E-filter, but all that light is pressed into one red channel anyway. In principle you let orange light count as red. I think that someone imaging from a light polluted site should more carefully examine the filters. But in that case equalising fluxes is of less concern. I can imagine that if  comparing the various filters, you'd say that one set gives "cleaner" or "crisper" or "more saturated" results, but that may depend more on other characteristics than bandwidth. E.g. reflections or glass quality.

Adding Ha to the mix, offsets the balance, as you noted.

[John78]

So I still haven't actually ordered the camera - its frustrating that ZWO have put the camera on sale, every US vendor has mirrored that sale price of $1180 and the UK vendors are resolute in demanding £1309 in unison - with the new camera arriving to replace it next month and the new Atik Horizon to begin shipping when is the price coming down??  

Edit : to add you can buy one from a US vendor next day delivered, with import duty paid for £1116 - its not right.

 

[Lee_P]

To say the learning curve is steep is an understatement, but I've finally produced a photo not destined for the recycle bin. This and other SGL threads were invaluable in getting to this stage. Onward and upward!

 

[alcol620]

Hi Lee

 

Nice image. Not sure what your camera Gain setting was but the following link is a good read on the capability and benefits of taking short exposures with the ASI1600 camera. Keep up the good work

[Lee_P]

5 minutes ago, alcol620 said:

Hi Lee

 

Nice image. Not sure what your camera Gain setting was but the following link is a good read on the capability and benefits of taking short exposures with the ASI1600 camera. Keep up the good work

Thanks! I've been shooting Gain 300, five-minute exposures. Do you think that I should change this? (I can't see the link you refer to..?)

[alcol620]

10 minutes ago, alcol620 said:

Hi Lee

 

Nice image. Not sure what your camera Gain setting was but the following link is a good read on the capability and benefits of taking short exposures with the ASI1600 camera. Keep up the good work

OOOPs forgot to put the link in  https://www.cloudynights.com/topic/570020-gain-settings-for-asi1600mm-cool/page-2

[alcol620]

All very complicated, trying to fathom it myself

[Gina]

I've used short exposures of around 60s with very high gain (up to 600 - 60dB) and hundreds of them, for DSOs, processed in PixInsight, with good results.  Needs a fast computer!

[Guest]

15 hours ago, Lee_P said:

Thanks! I've been shooting Gain 300, five-minute exposures. Do you think that I should change this? (I can't see the link you refer to..?)

Nice shot of this object :-)

I use 139 gain, 10 Offset, 60 sec for L, 120 sec for RGB and 5 min for narrow band and love the results I get :-)

Hope that helps

David

[Demonperformer]

On Wednesday, October 18, 2017 at 11:32, Gina said:

I've used short exposures of around 60s with very high gain (up to 600 - 60dB) and hundreds of them, for DSOs, processed in PixInsight, with good results.  Needs a fast computer!

Gina, Are those figures for LRGB or NB?

Thanks.

[Gina]

NB with Astrodon 3nm filters.

[SyedT]

After Cygnus disappeared behind the house last night, I switched over to shooting the HorseHead and Flame Nebulae, and am I glad I did. 

Below is a composite of 56x300" subs in Ha; no calibration frames applied, no editing, just a simple autostretch in Pixinsight to make the image non-linear. The noise profile blew me away, I have to say!

Equipment: ASI 1600MM-C + Baader Ha 7nm 2" filter + WO GT81 with 0.8x FF/FR

[Rico]

@SyedTI made the same decision  last night. Started off on the crescent nebula and then moved over to the horsehead as soon as it disappeared behind the house. I managed 4.5 hours ha 6nm on my modified 700d swed80 combo. I'm on the verge of crossing over to a mono, so that image you posted really helps. The WO is about a stop quicker, and we may have differences in sky quality, but still ... thanks for posting. Great result btw!

[SyedT]

17 minutes ago, Rico said:

@SyedTI made the same decision  last night. Started off on the crescent nebula and then moved over to the horsehead as soon as it disappeared behind the house. I managed 4.5 hours ha 6nm on my modified 700d swed80 combo. I'm on the verge of crossing over to a mono, so that image you posted really helps. The WO is about a stop quicker, and we may have differences in sky quality, but still ... thanks for posting. Great result btw!

Thanks Rico, appreciate. I'm new to mono imaging myself, and wouldn't change a thing now; imaging under the full moon is a blessing, especially when clear skies here are a rarity. Yes it can take more time and planning and the processing can be a pain sometimes, but the results have definitely been worth it so far! The sensitivity of the 1600MM-C continues to impress me as well, and one can recover quite a few bits by stacking at least 64 images.

[souls33k3r]

12 hours ago, SyedT said:

After Cygnus disappeared behind the house last night, I switched over to shooting the HorseHead and Flame Nebulae, and am I glad I did. 

Below is a composite of 56x300" subs in Ha; no calibration frames applied, no editing, just a simple autostretch in Pixinsight to make the image non-linear. The noise profile blew me away, I have to say!

Equipment: ASI 1600MM-C + Baader Ha 7nm 2" filter + WO GT81 with 0.8x FF/FR

Very nice indeed. What gain and offset setting did you use for this?

[SyedT]

2 hours ago, souls33k3r said:

Very nice indeed. What gain and offset setting did you use for this?

Cheers! Unity gain 139 and Offset 21.

[alcol620]

7 hours ago, SyedT said:

Cheers! Unity gain 139 and Offset 21.

Could up the gain and reduce the exposure?

[SyedT]

38 minutes ago, alcol620 said:

Could up the gain and reduce the exposure?

I've tried that, wasn't liking how the images were turning out. I'm just going with unity gain and stacking at least 64 subs to recover enough bits; seems to work well so far. That being said, I'll probably go for 60-180s exposures for my RGB filters to avoid LP issues. 

[alcol620]

2 minutes ago, SyedT said:

I've tried that, wasn't liking how the images were turning out. I'm just going with unity gain and stacking at least 64 subs to recover enough bits; seems to work well so far.

See  https://www.cloudynights.com/topic/570020-gain-settings-for-asi1600mm-cool/page-2 background to NB higher gain/shorter exposures

[SyedT]

36 minutes ago, alcol620 said:

See  https://www.cloudynights.com/topic/570020-gain-settings-for-asi1600mm-cool/page-2 background to NB higher gain/shorter exposures

Thanks, I've already read Jon's evaluation of the 1600MM-C and was initially using his formula to calculate my optimal ADU values. I've found that exposures lower than 300s for my particular setup and processing routine don't fare too well when it comes to narrowband, so I've stuck with 300s; it's short enough to allow me to get 64 subs in a reasonable timeframe + makes for easy guiding, and long enough that I can pick up faint details and still preserve dynamic range by using a lower gain setting. I'm picking up around 700-900 ADU at unity gain, so pretty much optimal for exposure time.